Catalyst impregnated on fine silica, process for preparing, and use for ethylene polymerization

ABSTRACT

Film grade ethylene copolymers are prepared by copolymerizing ethylene with at least one C 3  to C 8  alpha olefin employing a catalyst formed from an organo aluminum activator compound and a precursor composition impregnated in very fine particle sized porous silica, said precursor composition having the formula 
     
         MG.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED.sub.q ] 
    
     wherein R is a C 1  to C 14  aliphatic or aromatic hydrocarbon radical, or COR&#39; wherein R&#39; is a C 1  to C 14  aliphatic or aromatic hydrocarbon radical; X is selected from the group consisting of Cl, Br, I or mixtures thereof; ED is an electron donor compound; m is ≧0.5 to ≦56; n is 0, 1 or 2; p is ≧2 to ≦116; and q is ≧2 to ≦85; and said organo aluminum activator compound having the formula 
     
         Al(R&#34;).sub.c X&#39;.sub.d H.sub.e 
    
     wherein X&#39; is Cl or OR&#39;&#34;; R&#34; and R&#39;&#34; are the same or different and are C 1  to C 14  saturated hydrocarbon radicals; d is 0 to 1.5; e is 1 or 0; and c+d+e=3.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 163,959,filed June 30, 1980, now U.S. Pat. No. 4,405,495.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the catalytic copolymerization of ethylene withhigh activity, silica supported, Mg and Ti containing catalysts in a gasphase process to produce film grade polymers.

2. Description of the Prior Art

European Patent Application No. 79-100958.2, filed Mar. 30, 1979 andpublished Oct. 17, 1979 as Publication No. 4647 (EPA Publication 4647),which corresponds to U.S. patent application Ser. No. 12,720, filed Feb.16, 1979 in the names of G. L. Goeke et al, now U.S. Pat. No. 4,302,565,discloses the catalytic copolymerization of ethylene with C₃ to C₈ alphaolefin comonomer to produce film grade resin in the gas phase withcertain high activity catalysts. These catalysts are formed from certainorgano aluminum compounds and certain precursor compounds. The precursorcompounds are formed from certain Ti compounds, Mg compounds andelectron donor (ED) compounds. The catalysts are impregnated in porousparticulate inert carrier materials. The preferred of such carriermaterials is silica.

When used with the particulate silica materials which have beencommercially available to date, however, these Ti/Mg/ED containingcatalysts have produced ethylene copolymers in the process described inEPA Publication 4647 which, while meeting most of the requirements forfilm grade resins, still have some deficiencies in the area of filmappearance, as measured by a film appearance rating (FAR), due to thepresence of gels and other visual imperfections. Thus, while copolymersmade by the process of EPA Publication 4647 tend to have an FAR valuewhich will satisfy the needs of many end use film applications for whichethylene polymers are used, certain film applications require the use offilms having even higher FAR values. Such latter applications wouldinclude uses where the films are to be employed for packaging and/or areto contain printed material.

Various attempts to improve the FAR values of the copolymers, in filmform, made with the high activity catalysts and process of EPAPublication 4647, by using one or the other of various types of inertporous supports with such catalysts in such process were not successful,prior to the present invention. Likewise, efforts to upgrade propertiessuch as bulk density, particle size, resin flowability and catalystproductivity, have met with little success.

SUMMARY OF THE INVENTION

It has now been unexpectedly found that ethylene copolymers which, infilm form, have excellent mechanical and optical properties, can beproduced at relatively high productivities for commercial purposes by agas phase process if the ethylene is copolymerized with one or more C₃to C₈ alpha olefins in the presence of a high activitymagnesium-titanium complex catalyst prepared, as described below, underspecific activation conditions with an organo aluminum compound andimpregnated in porous particulate silica having a relatively smallparticle size.

An object of the present invention is to provide a process forproducing, with relatively high productivities and in a low pressure gasphase process, ethylene copolymers which have, in the form of polymers,a relatively low residual catalyst content, a density of about 0.91 to0.94, a molecular weight distribution of about 2.5 to 6.0, a bulkdensity of about 23 to 35, small average resin particle size but lowresin fine content, good flow properties, and in film form, excellentFAR values and mechanical properties.

A further object of the present invention is to provide a process inwhich ethylene copolymers which are useful for a variety of end-use filmapplications may be readily prepared.

A still further object of the present invention is to provide a varietyof novel ethylene copolymers and film products made therefrom.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing shows a gas phase fluid bed reactor system in which thecatalyst system of the present invention may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It has now been found that the desired ethylene copolymers can bereadily produced with relatively high productivities in a low pressuregas phase fluid bed reaction process if the monomer charge ispolymerized under a specific set of operating conditions, as detailedbelow, and in the presence of a specific high activity catalyst which isimpregnated on a porous particulate silica of specified particle size,as is also detailed below.

THE ETHYLENE COPOLYMERS

The copolymers which may be prepared with the catalysts of the presentinvention are copolymers of a major mol percent (≧90%) of ethylene, anda minor mol percent (≧10%) of one or more C₃ to C₈ alpha olefins whichshould not contain any branching on any of their carbon atoms which iscloser than the fourth carbon atom. These alpha olefins includepropylene, butene-1, pentene-1, hexene-1, 4-methyl pentene-1, heptene-1and octene-1. The preferred alpha olefins are propylene, butene-1,hexene-1, 4-methyl pentene-1 and octene-1.

The copolymers have a molecular weight distribution of about 2.5 to 6.0,and preferably of about 2.7 to 4.1. The melt flow ratio (MFR) value isanother means of indicating the molecular weight distribution value(Mw/Mn) of a polymer. For the copolymers of the present invention, anMFR value range of ≧20 to ≦40 corresponds to a Mw/Mn value range ofabout 2.5 to 6.0, and an MFR value range of ≧22 to ≦32 corresponds to anMw/Mn value range of about 2.7 to 4.1.

The copolymers have a density of about ≧0.91 to ≦0.94, and preferably≧0.916 to ≦0.935. The density of the copolymer, at a given melt indexlevel for the copolymer, is primarily regulated by the amount of the C₃to C₈ comonomer which is copolymerized with the ethylene. In the absenceof the comonomer, the ethylene would homopolymerize with the catalyst ofthe present invention to provide homopolymers having a density of about≧0.96. Thus, the addition of progressively larger amounts of thecomonomers to the copolymers results in a progressive lowering of thedensity of the copolymer. The amount of each of the various C₃ to C₈comonomers needed to achieve the same result will vary from comonomer tocomonomer, under the same reaction conditions.

Thus, to achieve the same results, in the copolymers, in terms of agiven density, at a given melt index level, larger molar amounts of thedifferent comonomers would be needed in the order of C₃ >C₄ >C₅ >C₆ >C₇>C₈.

The copolymers made in the process of the present invention have astandard or normal load melt index of ≧0.0 to about 100, and preferablyof about 0.5 to 80, and a high load melt index (HLMI) of about 11 toabout 2000. The melt index of the copolymers which are made in theprocess of the present invention is a function of a combination of thepolymerization temperature of the reaction, the density of the copolymerand the hydrogen/monomer ratio in the reaction system. Thus, the meltindex is raised by increasing the polymerization temperature and/or bydecreasing the density of the copolymer and/or by increasing thehydrogen/monomer ratio. In addition to hydrogen, other chain transferagents such as dialkyl zinc compounds may also be used to furtherincrease the melt index of the copolymers.

The copolymers of the present invention have an unsaturated groupcontent of ≦1, and usually ≧0.1 to ≦0.3, C═C/1000 carbon atoms, and ann-hexane extractables content (at 50° C.) of less than about 3, andpreferably of less than about 2, weight percent.

As compared to the homogeneous copolymers of U.S. Pat. No. 3,645,992,the copolymers of the present invention are heterogeneous. They havemelting points of about ≧121° C.

The copolymers of the present invention have a residual catalystcontent, in terms of parts per million of titanium metal, of the orderof >0 to ≦10 parts per million (ppm) at a productivity level of≧100,000, of the order of >0 to ≦5 ppm at a productivity level of≧200,000, and of the order of >0 to ≦2 parts per million at aproductivity level of ≧500,000. The copolymers are readily produced inthe process of the present invention at productivities of up to about500,000.

The copolymers of the present invention are granular materials whichhave an average particle size of the order of about 0.01 to about 0.04inches, and preferably of about 0.02 to about 0.03 inches, in diameter.The particle size is important for the purposes of readily fluidizingthe polymer particles in the fluid bed reactor, as described below. Thegranular copolymers of the present invention have a bulk density ofabout 23 to 25 pounds per cubic foot.

In addition to being useful for making film therefrom the copolymers ofthe present invention are useful in other molding applications.

For film making purposes the preferred copolymers of the presentinvention are those having a density of about ≧0.916 to ≦0.935, andpreferably of about ≧0.917 to ≦0.928; a molecular weight distribution(Mw/Mn) of ≧2.7 to ≦4.1, preferably of about ≧2.8 to 3.1; and a standardmelt index of >0.5 to ≦5.0, and preferably of about ≧0.7 to ≦4.0. Thefilms have a thickness of >0 to ≦10 mils, and preferably of >0 to ≦5mils, and more preferably of >0 to ≦1 mil.

For the injection molding of flexible articles such as housewarematerials, the preferred copolymers of the present invention are thosehaving a density of ≧0.920 to ≦0.940, and preferably of about ≧0.925 to≦0.930; a molecular weight distribution Mw/Mn of ≧2.7 to ≦3.6, andpreferably of about ≧2.8 to ≦3.1; and a standard melt index of ≦2 to≧100 and preferably of about ≧8 to ≦80.

HIGH ACTIVITY CATALYST

The compounds used to form the high activity catalyst used in thepresent invention comprise at least one titanium compound, at least onemagnesium compound, at least one electron donor compound, at least oneactivator compound and at least one silica material, as defined below.

The titanium compound has the structure

    Ti(OR).sub.a X.sub.b

wherein R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, orCOR' where R' is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical,

X is selected from the group consisting of Cl, Br, I or mixturesthereof,

a is 0, 1 or 2, b is 1 to 4 inclusive and a+b=3 or 4.

The titanium compounds can be used individually or in combinationsthereof, and would include TiCl₃, TiCl₄, Ti(OCH₃)Cl₃, Ti(OC₆ H₅)Cl₃,Ti(OCOCH₃)Cl₃ and Ti(OCOC₆ H₅)Cl₃.

The magnesium compound has the structure

    MgX.sub.2

wherein X is selected from the group consisting of Cl, Br, I or mixturesthereof. Such magnesium compounds can be used individually or incombinations thereof and would include MgCl₂, MgBr₂ and MgI₂. AnhydrousMgCl₂ is the particularly preferred magnesium compound.

About 0.5 to 56, and preferably about 1.5 to 5, mols of the magnesiumcompound are used per mol of the titanium compound in preparing thecatalysts employed in the present invention.

The titanium compound and the magnesium compound should be used in aform which will facilitate their dissolution in the electron donorcompound, as described herein below.

The electron donor compound is an organic compound which is liquid at25° C. and in which the titanium compound and the magnesium compound aresoluble. The electron donor compounds are known, as such, or as Lewisbases.

The electron donor compounds would include such compounds as alkylesters of aliphatic and aromatic carboxylic acids, aliphatic ethers,cyclic ethers and aliphatic ketones. Among these electron donorcompounds the preferable ones are alkyl esters of C₁ to C₄ saturatedaliphatic carboxylic acids; alkyl esters of C₇ to C₈ aromatic carboxylicacids; C₂ to C₈, and preferably C₃ to C₄, aliphatic ethers; C₃ to C₄cyclic ethers, and preferably C₄ cyclic mono- or di-ethers; C₃ to C₆,and preferably C₃ to C₄, aliphatic ketones. The most preferred of theseelectron donor compounds would include methyl formate, ethyl acetate,butyl acetate, ethyl ether, hexyl ether, tetrahydrofuran, dioxane,acetone and methyl isobutyl ketone.

The electron donor compounds can be used individually or in combinationsthereof.

About 2 to 85, preferably about 3 to 10 mols of the electron donorcompound are used per mol of Ti.

The activator compound has the structure

    Al(R").sub.c X'.sub.d H.sub.e

wherein

X' is Cl, or OR"',

R" and R"' are the same or different and are C₁ to C₁₄ saturatedhydrocarbon radicals,

d is 0 to 1.5, e is 1 or 0 and c+d+e=3.

Such activator compounds can be used individually or in combinationsthereof and would include Al(C₂ H₅)₃, Al(C₂ H₅)₂ Cl, Al(i-C₄ H₉)₃, Al₂(C₂ H₅)₃ Cl₃, Al(i-C₄ H₉)₂ H, Al(C₆ H₁₃)₃, Al(C₈ H₁₇)₃, Al(C₂ H₅)₂ H andAl(C₂ H₅)₂ (OC₂ H₅).

About 10 to 400, and preferably about 15 to 60, mols of the activatorcompound are used per mol of the titanium compound in activating thecatalysts employed in the present invention.

The silica support which is employed in the present invention shouldhave a particle size distribution within the range of from 2 microns tono more than 80 microns, and should have an average particle size offrom 20 microns to 50 microns. Preferably such silica support has aparticle size distribution of from 5 microns to no more than 65 microns,and an average particle size of from 25 microns to 45 microns. As thesize of the support decreases, the productivity of the supportedcatalyst system increases, as does the FAR value of film formed fromresin produced by the system. This is accompanied by an increase in thebulk density and a decrease in the average particle size of such resin.However, as the support size decreases to below 5 microns, an excessiveamount of very fine particle size resin (<50 microns) may be producedwhich can cause operational difficulties in the fluid bed reactor. Amongsuch difficulties are coating of the reactor walls and plugging ofpressure taps with these fine resin particles, as well as entrainmentand recycling of such fines in the reactor. For this reason, no morethan 5 percent by weight of the silica should have a particle size below5 microns. It is also preferred that no more than 15 percent by weightof the silica should have a particle size below 10 microns. Likewise, inorder to maximize the advantages of the invention, it is preferred thatno more than 10 percent by weight of the silica have a particle sizegreater than 65 microns.

Most desirably, the silica support employed in the present invention hasan average pore diameter of greater than 100 Angstrom units, andpreferably greater than 150 Angstrom units. It is also desirable forsuch silica support to have a surface area of ≧200 square meters pergram, and preferably ≧250 square meters per gram. The average porevolume of such silica is preferably from 1.4 ml/g. to 1.8 ml/g.

The carrier material should be dry, that is, free of absorbed water.Drying of the carrier material is carried out by heating it at atemperature of ≧600° C. Alternatively, the carrier material dried at atemperature of ≧200° C. may be treated with about 1 to 8 weight percentof one or more of the aluminum alkyl compounds described above. Themodification of the support by the aluminum alkyl compounds provides thecatalyst composition with increase activity and also improves polymerparticle morphology of the resulting ethylene polymers.

CATALYST PREPARATION: FORMATION OF PRECURSOR

The catalyst used in the present invention is prepared by firstpreparing a precursor composition from the titanium compound, themagnesium compound, and the electron donor compound, as described below,and then impregnating the carrier material with the precursorcomposition and then treating the impregnated precursor composition withthe activator compound as described below.

The precursor composition is formed by dissolving the titanium compoundand the magnesium compound in the electron donor compound at atemperature of about 20° C. up to the boiling point of the electrondonor compound. The titanium compound can be added to the electron donorcompound before or after the addition of the magnesium compound, orconcurrent therewith. The dissolution of the titanium compound and themagnesium compound can be facilitated by stirring, and in some instancesby refluxing, these two compounds in the electron donor compound. Afterthe titanium compound and the magnesium compound are dissolved, theprecursor composition may be isolated by crystallization or byprecipitation with a C₅ to C₈ aliphatic or aromatic hydrocarbon such ashexane, isopentane or benzene. The crystallized or precipitatedprecursor composition may be isolated, in the form of fine, free flowingparticles having an average particle size of about 10 to 100 microns.

When thus made as disclosed above the precursor composition has theformula

    Mg.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED].sub.q

wherein

ED is the electron donor compound,

m is ≧0.5 to ≦56, and preferably ≧1.5 to ≦5,

n is 0, 1 or 2,

p is ≧2 to ≦116, and preferably ≧6 to ≦14,

q is ≧2 to ≦85, and preferably ≧3 to ≦10,

R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, or COR'

wherein

R' is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical and,

X is selected from the group consisting of Cl, Br, I or mixturesthereof.

The subscript for the element titanium (Ti) is the arabic numeral one.

CATALYST PREPARATION: IMPREGNATION OF PRECURSOR IN SUPPORT

The precursor composition is then impregnated, in a weight ratio ofabout 0.033 to 1, and preferably about 0.1 to 0.33, parts of theprecursor composition into one part by weight of the carrier material.

The impregnation of the dried (activated) support with the precursorcomposition may be accomplished by dissolving the precursor compositionin the electron donor compound, and by then admixing the support withthe precursor composition to impregnate the support. The solvent is thenremoved by drying at temperatures of ≧60° C.

The support may also be impregnated with the precursor composition byadding the support to a solution of the chemical raw materials used toform the precursor composition in the electron donor compound, withoutisolating the precursor composition from such solution. The excesselectron donor compound is then removed by drying or washing and dryingat temperatures of ≦60° C.

ACTIVATION OF PRECURSOR COMPOSITION

In order to be used in the process of the present invention theprecursor composition must be fully or completely activated, that is, itmust be treated with sufficient activator compound to transform the Tiatoms in the precursor composition to an active state.

It has been found that, in order to prepare a useful catalyst, it isnecessary to conduct the activation in such a way that at least thefinal activation stage must be conducted in the absence of solvent so asto avoid the need for drying the fully active catalyst to remove solventtherefrom.

The precursor composition is first partially activated outside thepolymerization reactor with enough activator compound so as to provide apartially activated precursor composition which has an activatorcompound/Ti molar ratio of about >0 to <10:1, and preferably of about 4to 8:1. This partial activation reaction is carried out in a hydrocarbonsolvent slurry followed by drying of the resulting mixture, to removethe solvent, at temperatures between 20° to 80° C., and preferably of50° to 70° C. The resulting product is a free-flowing solid particulatematerial which can be readily fed to the polymerization reactor. Thepartially activated and impregnated precursor composition is fed to thepolymerization reactor where the activation is completed with additionalactivator compound which can be the same or a different compound.

The additional activator compound and the partially activatedimpregnated precursor composition are preferably fed to the reactorthrough separate feed lines. The additional activator compound may besprayed into the reactor in the form of a solution thereof in ahydrocarbon solvent such as isopentane, hexane, or mineral oil. Thissolution usually contains about 2 to 30 weight percent of the activatorcompound. The additional activator compound is added to the reactor insuch amounts as to provide, in the reactor, with the amounts ofactivator compound and titanium compound fed with the partiallyactivated and impregnated precursor composition, a total Al/Ti molarratio of ≧10 to 400, and preferably of about 15 to 60. The additionalamounts of activator compound added to the reactor react with andcomplete the activation of the titanium compound in the reactor.

In a continuous gas phase process, such as the fluid bed processdisclosed below, discrete portions of the partially activated precursorcomposition impregnated on the support are continuously fed to thereactor, with discrete portions of additional activator compound neededto complete the activation of the partially activated precursorcomposition, during the continuing polymerization process in order toreplace active catalyst sites that are expended during the course of thereaction.

THE POLYMERIZATION REACTION

The polymerization reaction is conducted by contacting a stream of themonomer(s), in a gas phase process, such as in the fluid bed processdescribed below, and substantially in the absence of catalyst poisonssuch as moisture, oxygen, CO, CO₂ and acetylene with a catalyticallyeffective amount of the completely activated precursor composition (thecatalyst) at a temperature and at a pressure sufficient to initiate thepolymerization reaction.

In order to achieve the desired density ranges in the copolymers it isnecessary to copolymerized enough of the ≧C₃ comonomers with ethylene toachieve a level of >0 to 10 mol percent of the C₃ to C₈ comonomer in thecopolymer. The amount of comonomer needed to achieve this result willdepend on the particular comonomer(s) employed.

There is provided below a listing of the amounts, in mols, of variouscomonomers that are copolymerized with ethylene in order to providepolymers having the desired density range (within the range of about0.91 to 0.94) at any given melt index. The listing also indicates therelative molar concentration, of such comonomers to ethylene, which arein the recycled gas stream of monomers under reaction equilibriumconditions in the reactor.

    ______________________________________                                                                 Gas Stream                                                       mol % needed Comonomer/Ethylene                                   Comonomer   in copolymer molar ratio                                          ______________________________________                                        propylene   >0 to 10     >0 to 0.9                                            butene-1    >0 to 7.0    >0 to 0.7                                            pentene-1   >0 to 6.0    >0 to 0.45                                           hexene-1    >0 to 5.0    >0 to 0.4                                            octene-1    >0 to 4.5    >0 to 0.35                                           ______________________________________                                    

The catalyst system and process of the present invention may also beused to prepare the more specific film forming ethylene copolymers madewith three or more monomers which are disclosed in U.S. Pat. applicationSer. No. 049,555, filed June 18, 1979, now abandoned in the names of W.A. Fraser et al and entitled "High Tear Strength Polymers". Thesepolymers are hereinafter referred to as the HTS copolymers.

The HTS copolymers are interpolymers or copolymers of the monomers C₂,C_(a) and C_(b), wherein C₂ is ethylene, C_(a) is selected frompropylene, butene-1 and mixtures thereof, and C_(b) is selected from oneor more of the C₅ to C₈ alpha monoolefins which contain no branchingcloser than the fourth carbon atom. The C₅ to C₈ monomers includepentene-1, 4-methyl pentene-1, hexene-1, heptene-1 and octene-1. Thesepolymers are heterogeneous.

The C₂, C_(a) and C_(b) monomer units are believed to be randomlydistributed along the polymer chain in the HTS copolymers and do nothave the same ethylene/comonomer ratio among the polymer molecules. Themolar ratio of C_(a) /C₂ monomer units in the HTS copolymer mass isabout 0.006 to 0.09. The molar ratio of C_(b) /C₂ monomer units in theHTS copolymer mass is about 0.003 to 0.07. In addition, the C_(a) andC_(b) monomers are also used in such amounts in making the HTScopolymers as to provide in the copolymers a Branch Chain Factor valueof about 0.1 to 0.9, and preferably of about 0.2 to 0.8, where the##EQU1##

The HTS copolymers have a density of about 0.91 to 0.94, and preferablyof about 0.915 to 0.930, grams per cubic centimeter,

a melt flow ratio of ≧22 to ≦36, and preferably of about ≧25 to ≦32, and

a melt index of about 0.5 to 5.0, and preferably of about 0.8 to 4.0,decigrams per minute.

The melt flow ratio (MFR) range of ≧22 to ≦36 corresponds to a M_(w)/M_(n) value range of about 2.7 to 4.3, and the MFR range of ≧25 to ≦32corresponds to a Mw/Mn range of about 2.8 to 3.8.

In compression molded film form the HTS copolymers have a density ofabout 0.920 have an intrinsic (Elmendorf) tear strength of about 100 to800. In blown film form these HTS copolymers have an Elmendorft tearstrength of about 60 to 600 grams/mil.

The HTS copolymers have an unsaturated group content of ≦1, and usuallyof ≧0.1 to ≦0.6, C=C/1000 carbon atoms, and an n-hexane extractablescontent (at 50° C.) of less than about 5.5, and preferably, of less thanabout 4.0, weight percent.

Unless otherwise stated, as noted above, the HTS copolymers have otherproperties which are the same as the other copolymers discussed above.

A fluidized bed reaction system which can be used in the practice of theprocess of the present invention is illustrated in the drawing. Withreference thereto the reactor 1 consists of a reaction zone 2 and avelocity reduction zone 3.

The reaction zone 2 comprises a bed of growing polymer particles, formedpolymer particles and a minor amount of catalyst particles fluidized bythe continuous flow of polymerizable and modifying gaseous components inthe form of make-up feed and recycle gas through the reaction zone. Tomaintain a viable fluidized bed, the mass gas flow rate through the bedmust be above the minimum flow required for fluidization, and preferablyfrom about 1.5 to about 10 times G_(mf) and more preferably from about 3to about 6 times G_(mf). G_(mf) is used in the accepted form as theabbreviation for the minimum mass gas flow required to achievefluidization, C. Y. Wen and Y. H. Yu, "Mechanics of Fluidization",Chemical Engineering Progress Symposium Series, Vol. 62, p. 100-111(1966).

It is essential that the bed always contains particles to prevent theformation of localized "hot spots" and to entrap and distribute theparticulate catalyst throughout the reaction zone. On start up, thereactor is usually charged with a base of particulate polymer particlesbefore gas flow is initiated. Such particles may be identical in natureto the polymer to be formed or different therefrom. When different, theyare withdrawn with the desired formed polymer particles as the firstproduct. Eventually, a fluidized bed of the desired polymer particlessupplants the start-up bed.

The partially activated precursor composition (impregnated on the SiO₂support) used in the fluidized bed is preferably stored for service in areservoir 4 under a blanket of a gas which is inert to the storedmaterial, such as nitrogen or argon.

Fluidization is achieved by a high rate of gas recycle to and throughthe bed, typically in the order of about 50 times the rate of feed ofmake-up gas. The fluidized bed has the general appearance of a densemass of viable particles in possible free-vortex flow as created by thepercolation of gas through the bed. The pressure drop through the bed isequal to or slightly greater than the mass of the bed divided by thecross-sectional area. It is thus dependent on the geometry of thereactor.

Make-up gas is fed to the bed at a rate equal to the rate at whichparticulate polymer product is withdrawn. The composition of the make-upgas is determined by a gas analyzer 5 positioned above the bed. The gasanalyzer determines the composition of the gas being recycled and thecomposition of the make-up gas is adjusted accordingly to maintain anessentially steady state gaseous composition within the reaction zone.

To insure complete fluidization, the recycle gas and, where desired,part of the make-up gas are returned over gas recycle line 6 to thereactor at point 7 below the bed. At that point there is a gasdistribution plate 8 above the point of return to aid in fluidizing thebed.

The portion of the gas stream which does not react in the bedconstitutes the recycle gas which is removed from the polymerizationzone, preferably by passing it into a velocity reduction zone 3 abovethe bed where entrained particles are given an opportunity to drop backinto the bed.

The recycle gas is then compressed in a compressor 9 and then passedthrough a heat exchanger 10 wherein it is stripped of heat of reactionbefore it is returned to the bed. The temperature of the bed iscontrolled at an essentially constant temperature under steady stateconditions by constantly removing heat of reaction. No noticeabletemperature gradient appears to exist within the upper portion of thebed. A temperature gradient will exist in the bottom of the bed in alayer of about 6 to 12 inches, between the temperature of the inlet gasand the temperature of the remainder of the bed. The recycle is thenreturned to the reactor at its base 7 and to the fluidized bed throughdistribution plate 8. The compressor 9 can also be placed downstream ofthe heat exchanger 10.

The distribution plate 8 plays an important role in the operation of thereactor. The fluidized bed contains growing and formed particulatepolymer particles as well as catalyst particles. As the polymerparticles are hot and possibly active, they must be prevented fromsettling, for if a quiescent mass is allowed to exist, any activecatalyst contained therein may continue to react and cause fusion.Diffusing recycle gas through the bed at a rate sufficient to maintainfluidization throughout the bed is, therefore, important. Thedistribution plate 8 serves this purpose and may be a screen, slottedplate, perforated plate, a plate of the bubble cap type and the like.The elements of the plate may all be stationary, or the plate may be ofthe mobile type disclosed in U.S. Pat. No. 3,298,792. Whatever itsdesign, it must diffuse the recycle gas through the particles at thebase of the bed to keep the bed in a fluidized condition, and also serveto support a quiescent bed of resin particles when the reactor is not inoperation. The mobile elements of the plate may be used to dislodge anypolymer particles entrapped in or on the plate.

Hydrogen may be used as a chain transfer agent in the polymerizationreaction of the present invention. The ratio of hydrogen/ethyleneemployed will vary between about 0 to about 2.0 moles of hydrogen permole of the monomer in the gas stream.

Any gas inert to the catalyst and reactants can also be present in thegas stream. The activator compound is preferably added to the reactionsystem downstream from heat exchanger 10. Thus, the activator compoundmay be fed into the gas recycle system from dispenser 11 thru line 12.

Compounds of the structure Zn(R_(a)) (R_(b)), wherein R_(a) and R_(b)are the same or different C₁ to C₁₄ aliphatic or aromatic hydrocarbonradicals, may be used in conjunction with hydrogen, with the catalystsof the present invention, as molecular weight control or chain transferagents, that is, to increase the melt index values of the copolymersthat are produced. About 0 to 100, and preferably about 20 to 30 molesof the Zn compound (as Zn) would be used in the gas stream in thereactor per mol of titanium compound (as Ti) in the reactor. The zinccompound would be introduced into the reactor, preferably in the form ofa dilute solution (2 to 30 weight percent) in a hydrocarbon solvent orabsorbed on a solid diluent material, such as silica, in amounts ofabout 10 to 50 weight percent. These compositions tend to by pyrophoric.The zinc compound may be added alone, or with any additional portions ofthe activator compound that are to be added to the reactor, from afeeder, not shown, which could be positioned adjacent dispenser 11.

It is essential to operate the fluid bed reactor at a temperature belowthe sintering temperature of the polymer particles to insure thatsintering will not occur. For the production of the ethylene copolymersin the process of the present invention an operating temperature ofabout 30° to 105° C. is generally employed. Temperatures of about 70° to95° C. are used to prepare products having a density of about 0.91 to0.92, and temperatures of about 80° to 100° C. are used to prepareproducts having a density of about >0.92 to 0.94.

The fluid bed reactor is operated at pressures of up to about 1000 psi,and is preferably operated at a pressure of from about 150 to 400 psi,with operation at the higher pressures in such ranges favoring heattransfer since an increase in pressure increases the unit volume heatcapacity of the gas.

The partially activated and SiO₂ supported precursor composition isinjected into the bed at a rate equal to its consumption at a point 13which is above the distribution plate 8. Preferably, the catalyst isinjected at a point in the bed where good mixing of polymer particlesoccurs. Injecting the catalyst at a point above the distribution plateis an important feature of this invention. Since the catalysts used inthe practice of the invention are highly active, injection of thecatalyst into the area below the distribution plate may causepolymerization to begin there and eventually cause plugging of thedistribution plate. Injection into the viable bed, instead, aids indistributing the catalyst throughout the bed and tends to preclude theformation of localized spots of high catalyst concentration which mayresult in the formation of "hot spots". Injection of the catalyst intothe reactor above the bed may result in excessive catalyst carryoverinto the recycle line where polymerization may begin and plugging of theline and heat exchanger may eventually occur.

A gas which is inert to the catalyst, such as nitrogen or argon, is usedto carry the partially reduced precursor composition, and any additionalactivator compound or non-gaseous chain transfer agent that is needed,into the bed.

The production rate of the bed is controlled by the rate of catalystinjection. The production rate may be increased by simply increasing therate of catalyst injection and decreased by reducing the rate ofcatalyst injection.

Since any change in the rate of catalyst injection will change the rateof generation of the heat of reaction, the temperature of the recyclegas entering the reactor is adjusted upwards and downwards toaccommodate the change in rate of heat generation. This insures themaintenance of an essentially constant temperature in the bed. Completeinstrumentation of both the fluidized bed and the recycle gas coolingsystem is, of course, necessary to detect any temperature change in thebed so as to enable the operator to make a suitable adjustment in thetemperature of the recycle gas.

Under a given set of operating conditions, the fluidized bed ismaintained at essentially a constant height by withdrawing a portion ofthe bed as product at a rate equal to the rate of formation of theparticulate polymer product. Since the rate of heat generation isdirectly related to product formation, a measurement of the temperaturerise of the gas across the reactor (the difference between inlet gastemperature and exit gas temperature) is determinative of the rate ofparticulate polymer formation at a constant gas velocity.

The particulate polymer product is preferably continuously withdrawn ata point 14 at or close to the distribution plate 8 and in suspensionwith a portion of the gas stream which is vented as the particles settleto minimize further polymerization and sintering when the particlesreach their ultimate collection zone. The suspending gas may also beused to drive the product of one reactor to another reactor.

The particulate polymer product is conveniently and preferably withdrawnthrough the sequential operation of a pair of timed valves 15 and 16defining a segregation zone 17. While valve 16 is closed, valve 15 isopened to emit a plug of gas and product to the zone 17 between it andvalve 15 which is then closed. Valve 16 is then opened to deliver theproduct to an external recovery zone. Valve 16 is then closed to awaitthe next product recovery operation. The vented gas containing unreactedmonomers may be recovered from zone 17 through line 18 and recompressedin compressor 19 and returned directly, or through a purifier 20, overline 21 to gas recycle line 6 at a point upstream of the recyclecompressor 9.

Finally, the fluidized bed reactor is equipped with an adequate ventingsystem to allow venting the bed during start up and shut down. Thereactor does not required the use of stirring means and/or wallscrapping means. The recycle gas line 6 and the elements therein(compressor 9, heat exchanger 10) should be smooth surfaced, and devoidof unnecessary obstructions so as not to impede the flow of recycle gas.

The highly active catalyst system of this invention yield a fluid bedproduct having an average particle size of about 0.01 to about 0.04inches, and preferably about 0.02 to about 0.03 inches, in diameterwherein the catalyst residue is unusually low. The polymer particles arerelatively easy to fluidize in a fluid bed.

The feed stream of gaseous monomer, with or without inert gaseousdiluents, is fed into the reactor at a space time yield of about 2 to 10pounds/hour/cubic foot of bed volume.

The term virgin resin or polymer as used herein means polymer, ingranular form, as it is recovered from the polymerization reactor.

The catalysts of the present invention may also be used in the gas phasereaction process and apparatus disclosed in U.S. patent application Ser.No. 964,989, entitled "Exothermic Polymerization In A Vertical Fluid BedReactor System Containing Cooling Means Therein And Apparatus Therefor",and filed Nov. 30, 1978, now U.S. Pat. No. 4,255,542 in the names ofGary L. Brown et al, and which corresponds to European PatentApplication No. 79101169.5, which was filed Apr. 17, 1979 and which waspublished on Oct. 31, 1979 as Publication No. 4966. These applicationsdisclose the use of an entirely straight sided fluid bed reactor whichemploys heat exchange means within the reactor. The disclosures in thesepatent applications are incorporated herein by reference.

The following Examples are designed to illustrate the process of thepresent invention and are not intended as a limitation upon the scopethereof.

The properties of the polymers produced in the Examples were determinedby the following test methods:

Density: A plaque is made and conditioned for one hour at 100° C. toapproach equilibrium crystallinity. Measurement for density is then madein a density gradient column and density values are reported asgrams/cm³.

Melt Index (MI): ASTM D-2338--Condition E--Measured at 190° C.--reportedas grams per 10 minutes.

Flow Index (HLMI): ASTM D-1238--Condition F--Measured at 10 times theweight used in the melt index test above. ##EQU2##

Productivity: A sample of the resin product is ashed, and the weight %of ash is determined; since the ash is essentially composed of thecatalyst, the productivity is thus the pounds of polymer produced perpound of total catalyst consumed. The amount of Ti, Mg and halide in theash are determined by elemental analysis.

Bulk Density: ASTM D-1895 Method B. The resin is poured via 3/8"diameter funnel into a 400 ml graduated cylinder to 400 ml line withoutshaking the cylinder, and weighed by difference.

Molecular Weight Distribution (Mw/Mn): Gel Permeation ChromatographyStyrogel Packing: (Pore Size Sequence is 10⁷, 10⁵, 10⁴, 10³, 60 Å)Solvent is Perchloroethylene at 117° C. Detection: Infra red at 3.45μ.

Film Appearance Rating (FAR): A sample of film is viewed with the nakedeye to note the size and distribution of gels or other foreign particlesin comparison to standard film samples. The appearance of the film asthus compared to the standard samples is then given a rating on a scaleof -100 (very poor) to +100 (excellent).

n-hexane extractables: (FDA test used for polyethylene film intended forfood contact applications). A 200 square inch sample of 1.5 mil gaugefilm is cut into strips measuring 1"×6" and weighed to the nearest 0.1mg. The strips are placed in a vessel and extracted with 300 ml ofn-hexane at 50±1° C. for 2 hours. The extract is then decanted intotared culture dishes. After drying the extract in a vacuum desiccator,the culture dish is weighed to the nearest 0.1 mg. The extractables,normalized with respect to the original sample weight, is then reportedas the weight fraction of n-hexane extractables.

Unsaturation: Infrared Spectrophotometer (Perkin Elmer Model 21).Pressings made from the resin which are 25 mils in thickness are used astest specimens. Absorbance is measured at 10.35μ for transvinylideneunsaturation, 11.0μ for terminal vinyl unsaturation, and 11.25μ forpendant vinylidene unsaturation. The absorbance per mil of thickness ofthe pressing is directly proportional to the product of unsaturationconcentration and absorbtivity. Absorbtivities are taken from theliterature values of R. J. de Kock, et al., J. Polymer Science, Part B,2, 339 (1964).

Average Particle Size: This is calculated from sieve analysis datameasured according to ASTM-D-1921 Method A using a 500 g sample.Calculations are based on weight fractions retained on the screens.

1a. Preparation of Impregnated Precursor

In a 12 liter flask equipped with a mechanical stirrer are placed 41.8 g(0.439 mol) anhydrous MgCl₂ and 2.5 liter tetrahydrofuran (THF). To thismixture, 27.7 g (0.146 mol) TiCl₄ is added dropwise over 1/2 hour. Itmay be necessary to heat the mixture to 60° C. for about 1/2 hour inorder to completely dissolve the material.

The precursor composition can be isolated from solution bycrystallization or precipitation. It may be analyzed at this point forMg and Ti content since some of the Mg and/or Ti compound may have beenlost during the isolation of the precursor composition. The empiricalformulas used herein in reporting the precursor compositions are derivedby assuming that the Mg and the Ti still exist in the form of thecompounds in which they were first added to the electron donor compound.The amount of electron donor is determined by chromatography.

500 g of the silica support, dehydrated to 600° C. to 800° C. andtreated with 1 to 8 wt. % triethyl aluminum, is added to the abovesolution and stirred for 1/4 hour. The mixture is dried with a N₂ purgeat 60° C. to 80° C. for about 3-5 hours to provide a dry free flowingpowder having the particle size of the silica. The absorbed precursorcomposition has the formula

    TiMg.sub.3.0 Cl.sub.10 (THF).sub.6-8

1b. Preparation of Impregnated Precursor from Preformed PrecursorComposition

In a 12 liter flask equipped with a mechanical stirrer, 130 g ofprecursor composition is dissolved in 2.5 liters dry THF. The solutionmay be heated to 60° C. in order to facilitate dissolution. 500 g of thesilica support, dehydrated to 600° C. to 800° C. and treated with 1 to 8wt % triethyl aluminum, is added and the mixture is stirred for 1/4hour. The mixture is dried with a N₂ purge at 60° C. to 80° C. for about3-5 hours to provide a dry free flowing powder having the particle sizeof the silica.

II. Activation Procedure

The desired weights of impregnated precursor composition and activatorcompound are added to a mixing tank with sufficient amounts of anhydrousaliphatic hydrocarbon diluent such as isopentane to provide a slurrysystem.

The activator compound and precursor compound are used in such amountsas to provide a partially activated precursor composition which has anAl/Ti ratio of >0 to <10:1 and preferably of 4 to 8:1.

The contents of the slurry system are then thoroughly mixed at roomtemperature and at atmospheric pressure for about 1/4 to 1/2 hour. Theresulting slurry is then dried under a purge of dry inert gas, such asnitrogen or argon, at atmospheric pressure and at a temperature of65±10° C. to remove the hydrocarbon diluent. This process usuallyrequires about 3 to 5 hours. The resulting catalyst is in the form of apartially activated precursor composition which is impregnated withinthe pores of the silica. The material is a free flowing particulatematerial having the size and shape of the silica. It is not pyrophoricunless the aluminum alkyl content exceeds a loading of 10 weightpercent. It is stored under a dry inert gas, such as nitrogen or argon,prior to future use. It is now ready for use and injected into, andfully activated within, the polymerization reactor.

When additional activator compound is fed to the polymerization reactorfor the purpose of completing the activation of the precursorcomposition, it is fed into the reactor as a dilute solution in ahydrocarbon solvent such as isopentane. These dilute solutions containabout 2 to 30% by weight of the activator compound.

The activator compound is added to the polymerization reactor so as tomaintain the Al/Ti ratio in the reactor at a level of about ≧10 to400:1, and preferably of 15 to 60:1.

EXAMPLES 1 to 6

Ethylene was copolymerized with butene-1 in each of this series of 6examples.

In each of the examples, the catalyst used was formed as described abovein preparation Ia so as to form a silica impregnated catalyst systemcontaining 20% to 23% of precursor composition. The silica used inExample 1 was unscreened MS 1D Grade 952 silica available from DavisonChemical Divison, W. R. Grace and Company. The silica of Example 2 was acoarse fraction of Davison MS 1D Grade 952 silica which afterfractionation was retained on 60, 80 and 120 mesh size U.S. Standardscreens. Examples 3 employed a fine fraction of the Davison MS 1D Grade952 silica which had passed through a 230 mesh size U.S. Standardscreen. Examples 4, 5 and 6 employed unscreened Crosfield Company Ltd.'sGrade EP-10 silica, Akzo Chemie Ltd.'s "Ketjen" Grade F-7 silica, andU.S.I. Chemical Co.'s "Polypor" silica, respectively ("Ketjen" and"Polypor" are registered trademarks). The silica carriers employed ineach of the examples, as well as the average particle size and particlesize distribution of such carriers, are summarized in Table I below,along with the titanium and tetrahydrofuran content of the impregnatedcarriers.

                                      TABLE I                                     __________________________________________________________________________    Example        1     2     3   4   5   6                                      __________________________________________________________________________    Silica Carrier (a)   (b)   (c) (d) (e) (f)                                    Screen analysis, weight %                                                     Screen size                                                                    60 mesh (297 microns)                                                                       0           0   0   0   0                                       80 mesh (177 microns)                                                                       5.0   100   0   8.4 12.0                                                                              9.7                                    120 mesh (125 microns)                                                                       5.5         0   27.0                                                                              16.0                                                                              23.0                                   170 mesh (88 microns)                                                                        20.0  0     0   41.8                                                                              31.0                                                                              39.1                                   230 mesh (63 microns)                                                                        34.5  0     0   18.4                                                                              21.0                                                                              17.1                                   325 mesh (44 microns)                                                                        17.5  0         4.1 11.0                                                                              6.4                                                               100                                                pan (<44 microns)                                                                            17.5  0         0.3 9.0 4.7                                    Average particle size, microns                                                               81    180   35  115 105 114                                    Impregnated Carrier                                                           Ti, mmol/g     0.234 0.242 0.236                                                                             0.234                                                                             0.242                                                                             0.221                                  THF, wt. %     12.94 9.93  9.14                                                                              11.22                                                                             10.07                                                                             10.86                                  __________________________________________________________________________     (a) Unscreened MS 1D Grade 952 (Davison Chemical Division, W. R. Grace an     Co.)                                                                          (b) Coarse fraction of MS 1D Grade 952                                        (c) Fine fraction of MS 1D Grade 952                                          (d) Unscreened Grade EP10 (Crosfield Company Ltd.)                            (e) Unscreened "Ketjen" F7 (Akzo Chemie Ltd.)                                 (f) Unscreened "Polypor" (U.S.I. Chemical Co.)                           

In each example, the silica impregnated precursor composition waspartially activated with tri-n-hexyl aluminum, as described in procedureII above, so as to provide a catalyst composition having an Al/Ti molratio of 5±1. The completion of the activation of the precursorcomposition in the polymerization reactor was accomplished with a 5% byweight solution of triethyl aluminum in isopentane so as to provide acompletely activated catalyst in the reactor with an Al/Ti mol ratio of25 to 40.

Each of the polymerization reactions was conducted for 48 hours at 85°C. and under a pressure of 300 psig, a gas velocity of about 3 to 6times Gmf, and a space time yield of about 4.8 to 6.5 in a fluid bedreactor system. The reaction system was as described in the drawingabove. It has a lower section 10 feet high and 131/2 inches in (inner)diameter, and an upper section which was 16 feet high and 231/2 inchesin (inner) diameter.

Table II below lists the butene-1/ethylene molar ratio and H₂ /ethylenemolar ratio and the space time yield (lbs/hr/ft³ of bed space) used ineach example, as well as the various properties of the polymers made insuch examples, and various properties of film samples made from suchpolymers.

                                      TABLE II                                    __________________________________________________________________________    Example      1    2    3    4    5    6                                       __________________________________________________________________________    Operating Conditions                                                          C.sub.4 /C.sub.2 mol ratio                                                                 0.382                                                                              0.365                                                                              0.356                                                                              0.347                                                                              0.352                                                                              0.344                                   H.sub.2 /C.sub.2 mol ratio                                                                 0.171                                                                              0.159                                                                              0.177                                                                              0.183                                                                              0.181                                                                              0.170                                   Space time yield                                                                           6.5  5.9  5.3  4.8  5.0  5.0                                     (lbs/hr/ft.sup.3 bed space)                                                   Polymer Properties                                                            Melt index   2.15 1.5  1.90 2.68 2.60 1.95                                    Melt flow ratio                                                                            25.7 27.2 24.5 28.5 24.3 26.1                                    Density (g/cc)                                                                             0.9212                                                                             0.9215                                                                             0.9229                                                                             0.9214                                                                             0.9223                                                                             0.9214                                  Ti, ppm      7    6    3    5    2    3                                       % ash        0.05 0.05 0.019                                                                              0.043                                                                              --   0.011                                   Granular Properties                                                           Bulk density, lbs/cu. ft.                                                                  21.0 21.5 25.1 16.7 17.2 24.5                                    Screen analysis, weight %                                                     Screen size                                                                   10 mesh (0.0110")                                                                          7.1  9.7  0.6  37.8 32.7 6.5                                     18 mesh (0.0555")                                                                          45.6 54.0 7.2  48.0 48.7 49.9                                    35 mesh (0.0278")                                                                          40.2 32.9 55.1 12.1 17.4 39.1                                    60 mesh (0.0139")                                                                          6.7  3.4  34.7 1.5  1.2  4.5                                     120 mesh (0.0070")                                                                         0.4  0    2.2  0.6  0    0                                       200 mesh (0.0041")                                                                         0    0    0.2  0    0    0                                       pan          0    0    0    0    0    0                                       Average particle size, in.                                                                 0.0453                                                                             0.0503                                                                             0.0249                                                                             0.0733                                                                             0.0683                                                                             0.0460                                  Film Properties                                                               Film appearance rating                                                                     -30  -30  +10  <-25 <-30 <-10                                                                >-30 >-40 >-20                                    __________________________________________________________________________

As compared to granular copolymers made in copending application Ser.No. 012,720, filed on Feb. 16, 1979 in the names of George LeonardGeoke, Burkhard Eric Wagner and Frederick John Karol, entitled"Impregnated Polymerization Catalyst, Process for Preparing, And Use ForEthylene Copolymerization", now U.S. Pat. No. 4,302,565, the copolymersof the present invention, in virgin powder form, and at a given densityand melt index, have a smaller average particle size, higher bulkdensities, and lower catalyst residues. In film form, the copolymersmade by the process of the present invention have improved filmproperties compared to the copolymers made in said copendingapplication.

EXAMPLES 7 to 9

Ethylene was copolymerized with butene-1 in each of these series ofexamples.

In these examples the procedure of Examples 1 to 6 was repeated at apressure of 400 psig employing various sized silica particles as theprecursor carrier. The silica used in Example 7 was unscreened DavisonMS 1D Grade 952 silica. The silica of Example 8 was a mid fraction ofDavison MS 1D Grade 952 silica which had passed though a 120 mesh sizeU.S. Standard screen and was retained on a 170 and 230 mesh size U.S.Standard screen. Example 9 employed a fine fraction of the Davison MS 1DGrade 952 silica which had passed through a 230 mesh size U.S. Standardscreen. The silica carriers employed in each of the examples, as well asthe average particle size and particle size distribution of suchcarriers, are summarized in Table III below, along with the titanium andtetrahydrofuran content of the impregnated carriers. Table IV belowlists the butene-1/ethylene molar ratio and H₂ /ethylene molar ratio andthe space time yield (lbs/hr/ft³ of bed space) used in each example, aswell as the various properties of the polymers made in such examples,and the various properties of film samples made from such polymers.

                  TABLE III                                                       ______________________________________                                        Example          7             8         9                                    ______________________________________                                        Silica Carrier   (a)           (b)       (c)                                  Screen Analysis, weight %                                                     Screen size                                                                   60 mesh (297 microns)                                                                          0             0         0                                    80 mesh (177 microns)                                                                          5.0           0         0                                    120 mesh (125 microns)                                                                         5.5           0         0                                    170 mesh (88 microns)                                                                          20.0                    0                                                                   100                                            230 mesh (63 microns)                                                                          34.5                    0                                    325 mesh (44 microns)                                                                          17.5          0                                                                                       100                                  pan (<44 microns)                                                                              17.5          0       Average particle size,                                                          81cr86s)35                           Impregnated Carrier                                                           Ti, mmol/g       0.235         0.231     0.230                                THF, wt. %       11.18         9.00      9.56                                 ______________________________________                                         (a) Unscreened MS 1D Grade 952 (Davison Chemical Division, W. R. Grace an     Co.)                                                                          (b) Mid fraction of MS 1D Grade 952                                           (c) Fine fraction of MS 1D Grade 952                                     

                  TABLE IV                                                        ______________________________________                                        Example        7         8         9                                          ______________________________________                                        Operating Conditions                                                          C.sub.4 /C.sub.2 mol ratio                                                                   0.352     0.366     0.353                                      H.sub.2 /C.sub.2 mol ratio                                                                   0.169     0.166     0.154                                      Space time yield                                                                             6.3       5.9       6.3                                        (lbs/hr/ft.sup.3 bed space)                                                   Polymer Properties                                                            Melt index     2.0       2.50      2.40                                       Melt flow ratio                                                                              24.3      25.2      23.7                                       Density (g/cc) 0.9223    0.9216    0.9221                                     Ti, ppm        2         5         3                                          % ash          0.026     0.068     0.04                                       Granular Properties                                                           Bulk density, lbs/cu. ft.                                                                    22.7      23.9      26.0                                       Screen analysis, weight %                                                     Screen size                                                                   10 mesh (0.0110")                                                                            15.5      0.4       0                                          18 mesh (0.0555")                                                                            52.9      27.4      7.9                                        35 mesh (0.0278")                                                                            28.7      55.5      54.1                                       60 mesh (0.0139")                                                                            2.9       16.2      36.4                                       120 mesh (0.0070")                                                                           0         0.5       1.6                                        200 mesh (0.0041")                                                                           0         0         0                                          pan            0         0         0                                          Average particle size, in.                                                                   0.0548    0.0333    0.0245                                     Film Properties                                                               Film appearance rating                                                                       -10       -20       +25                                        ______________________________________                                    

EXAMPLES 10 to 11

Ethylene was copolymerized with butene-1 in each of two examples.

In both examples the procedure of Examples 1 to 6 was repeated in alarge commercial reactor at a pressure of 270 psig employing differentsized silica particles as the precursor carrier. The silica used inExample 10 was unscreened Davison MS 1D Grade 952 silica. Example 11employed a fine fraction of the Davison MS 1D Grade 952 silica which hadbeen separated by air classification. The separated fraction was capableof passing through a 230 mesh size U.S. Standard screen. The silicacarriers employed in each of the examples, as well as the averageparticle size and particle size distribution of such carriers, aresummarized in Table V below, along with the titanium and tetrahydrofurancontent of the impregnated carriers. Table VI below lists thebutene-1/ethylene molar ratio and H₂ /ethylene molar ratio and the spacetime yield (lbs/hr/ft³ of bed space) used in each example, as well asthe various properties of the polymers made in such examples, and thevarious properties of film samples made from such polymers.

                  TABLE V                                                         ______________________________________                                        Example             10             11                                         ______________________________________                                        Silica Carrier      (a)            (b)                                        Screen analysis, weight %                                                     Screen size                                                                    60 mesh (297 microns)                                                                            0              0                                           80 mesh (177 microns)                                                                            5.0            0                                          120 mesh (125 microns)                                                                            5.5            0                                          170 mesh (88 microns)                                                                             20.0           0                                          230 mesh (63 microns)                                                                             34.5           0                                          325 mesh (44 microns)                                                                             17.5                                                                                         100                                        pan (<44 microns)   17.5                                                      Average particle size, microns                                                                    81             22                                         Impregnated Carrier                                                           Ti, mmol/g          0.215          0.217                                      THF, wt. %          10.0           9.6                                        ______________________________________                                         (a) Unscreened MS 1D Grade 952 (Davison Chemical Division, W. R. Grace an     Co.)                                                                          (b) Fine fraction of MS 1D Grade 952                                     

                  TABLE VI                                                        ______________________________________                                        Example            10       11                                                ______________________________________                                        Operating Conditions                                                          C.sub.4 /C.sub.2 mol ratio                                                                       0.47     0.48                                              H.sub.2 /C.sub.2 mol ratio                                                                       0.18     0.18                                              Space time yield   6.0      6.0                                               (lbs/hr/ft.sup.3 bed space)                                                   Polymer Properties                                                            Melt index         1.7      2.2                                               Melt flow ratio    26.5     26.0                                              Density (g/cc)     0.920    0.920                                             Ti, ppm            3        2                                                 % ash              0.031    0.020                                             Granular Properties                                                           Bulk density, lbs/cu. ft.                                                                        25.5     26.5                                              Screen analysis, weight %                                                     Screen size                                                                   10 mesh (0.0110")  4.0      3.2                                               18 mesh (0.0555")  36.1     8.4                                               35 mesh (0.0278")  36.4     24.4                                              60 mesh (0.0139")  17.0     40.4                                              120 mesh (0.0070") 6.0      20.9  200 mesh (0.0041") 0.5 2.6                  pan                0        0.1                                               Average particle size, in.                                                                       0.0379   0.0225                                            Film Properties                                                               Film appearance rating                                                                           0        +40                                               ______________________________________                                    

What is claimed is:
 1. In a process for producing ethylene copolymercontaining ≧90 mol percent of ethylene and ≦10 mol percent of one ormore C₃ to C₈ alpha olefins wherein said copolymer is produced ingranular form at a density of ≧0.91 to ≦0.94 with a Ti containingcatalyst at a productivity level of ≧5 ppm of titanium per million partsof copolymer by a process which comprises copolymerizing ethylene withat least one C₃ to C₈ alpha olefin in a reactor at a temperature ofabout 30° to 105° C. under a pressure of up to about 1000 psi in the gasphase by contacting the monomer charge with, in the presence of about 0to 2.0 mols of hydrogen per mol of ethylene in the gas phase reactionzone, particles of a catalyst composition comprising a precursorcomposition of the formula

    Mg.sub.m Ti.sub.1 (OR).sub.n X.sub.p [ED].sub.q

wherein R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, orCOR' wherein R' is a C₁ to C₁₄ aliphatic or aromatic hydrocarbonradical, X is selected from the group consisting of Cl, Br, I ormixtures thereof, ED is an electron donor compound, m is ≧0.5 to ≦56, nis 0, 1 or 2, p is ≧2 to ≦116, and q is ≧2 to ≦85, said precursorcomposition being impregnated in a porous support in a weight ratio of0.1:1 to 0.33:1 and being first partially activated outside of saidreactor with >0 to <10 mols of activator compound per mol of Ti in saidprecursor composition, and then completely activated in said reactorwith ≧10 to ≦400 mols of activator compound per mol of Ti in saidprecursor composition, said activator compound having the formula

    Al(R").sub.c X'.sub.d H.sub.e

wherein X' is Cl or OR"', R" and R"' are the same or different and areC₁ to C₁₄ saturated hydrocarbon radicals, d is 1 to 1.5, e is 1 or 0 andc+d+e=3, said electron donor compound being a liquid organic compound inwhich said precursor composition is soluble and which is selected fromthe group consisting of alkyl esters of aliphatic and aromaticcarboxylic acids, aliphatic ethers, cyclic ethers and aliphatic ketones,the improvement which comprises employing as said support throughout thepolymerization silica having a particle size distribution within therange of from 2 microns to 80 microns and an average particle size offrom 20 microns to 50 microns.
 2. A process as in claim 1 which isconducted in a fluid bed process.
 3. A process as in claim 2 in whichethylene is copolymerized with butene-1.
 4. A process as in claim 2wherein no more than 15 percent by weight of the silica support has aparticle size below 10 microns.
 5. A process as in claim 2 wherein nomore than 5 percent by weight of the silica support has a particle sizebelow 5 microns and no more than 10 percent by weight of the silicasupport has a particle size greater than 65 microns.
 6. A process as inclaim 5 wherein no more than 15 percent by weight of the silica supporthas a particle size below 10 microns.
 7. A process as in claim 2 whereinthe silica support has a particle size distribution within the range offrom 5 microns to 65 microns and an average particle size of from 25microns to 45 microns.
 8. A process as in claim 7 wherein no more than15 percent by weight of the silica support has a particle size below 10microns.
 9. A process as in any one of claims 2, 5 or 7 wherein thesource of the Mg in said composition comprises MgCl₂.
 10. A process asin claim 9 in which the electron donor compound comprises at least oneether.
 11. A process as in claim 9 in which the electron donor compoundcomprises tetrahydrofuran.
 12. A process as in any one of claims 2, 5 or7 wherein the source of the Mg in said composition comprises MgCl₂ andthe source of the Ti in said composition comprises TiCl₄.
 13. A processas in claim 12 in which the electron donor compound comprises at leastone ether.
 14. A process as in claim 12 in which the electron donorcompound comprises tetrahydrofuran.